It is well known that, the LED high bay light, of which the illuminant part and the optical lens are both of linear structure, is a kind of new high-power lighting fixture with a maximum length of 1100 mm emerged in the market of North America recently. However, the existing optical lens is of the structure of one-piece injection molding; thus the difficulty in and the expenses for making the mold and the cost for manufacturing the parts will be greatly increased as the requirement on the length of the optical lens increases.